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On 1/16/2012 1:34 PM, <a class="moz-txt-link-abbreviated" href="mailto:penobscotsolar@midmaine.com">penobscotsolar@midmaine.com</a> wrote:
<blockquote
cite="mid:beec43d1b4c0a3633e2e8d6fa9c27eab.squirrel@mail.myottmail.com"
type="cite">
<pre wrap="">Impressive, Bob, but if one 125 watt panel took 1000 watts of power, what
is it going to take to melt my two 1600 watt arrays, pole mounted,
(theoretically, of course, and at a 65 degree tilt)....? Just wondering as
it seems a lot of power to use in the winter for an off grid or solar
reliant system.
Thanks,
Daryl
</pre>
</blockquote>
<br>
<br>
Yes, it can take a lot of energy. How much and how long depends
on what<br>
the outside ambient temperature is. I think it will have a problem
in extreme<br>
cold because it depends on temperature rise of the module to get it
above freezing.<br>
If the sun comes out, that helps a lot so would help to reduce the
energy in melting.<br>
<br>
The melting we just now tried here, melted 2 X 200W modules
(series) in 45 minutes with 700 Watts<br>
of power into them (0.7 kW-hour) which is much better than my older
experiment and I believe<br>
being off the ground makes a big difference. The outside
temperature right now is only 31<br>
degrees F so kind of warm. The array is sitting at about 25 degree
tilt just above the metal<br>
roof on our building. It is still snowing here so no sun.<br>
<br>
Colder temperatures like the one in my animated gif will take longer
but I am sure that<br>
keeping them off the ground helps a lot. My 3 year old test was
sticking in the snow<br>
on the ground.<br>
<br>
There may be times though where it might be better to run some power
into an array that<br>
has a chance of melting while the generator has to run anyway. If
it didn't quite work then<br>
nothing much lost. Unless it has a chance of working fairly
quickly without too much energy<br>
from the batteries, you'd want to have a generator running. Todays
melting experiment<br>
was done off the batteries only.<br>
<br>
To have any gains, you would have to have some sun coming soon<br>
after it was melted off the array before it snowed again.<br>
<br>
This isn't a complete fix but something that may be put into the bag
of tricks<br>
when it does work to an advantage. Here it is still snowing so it
wouldn't<br>
make any difference but is sure fun to watch !<br>
<br>
<font face="Courier New, Courier, monospace"><br>
</font><font face="Courier New, Courier, monospace">
PS for </font><font color="navy" face="Courier New, Courier,
monospace" size="2"><span style="font-size: 10pt; font-family:
"Comic Sans MS"; color: navy;">Mark Dickson, I don't
know what it would take for your 50 watt module but much</span></font><br>
<font color="navy" face="Courier New, Courier, monospace" size="2"><span
style="font-size:10.0pt;font-family:"Comic Sans
MS";color:navy">
less power than for the 400 watts of PV we just melted snow on
in the same conditions.</span></font><br>
<br>
boB<br>
<br>
<br>
<blockquote
cite="mid:beec43d1b4c0a3633e2e8d6fa9c27eab.squirrel@mail.myottmail.com"
type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<pre wrap="">On 1/16/2012 11:39 AM, David Katz wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Mark,
I believe the Midnite Classic has this feature built in. Check with
them.
David Katz
</pre>
</blockquote>
<pre wrap="">
It just snowed up here in Arlington, Washington A.C. and we were just
starting to melt some snow
on a couple of modules on our roof just now with one of our charge
controllers here in the lab.
This feature is not yet in the Classic, BUT, check out this experiment
that I did about 3 years ago
in my front yard with an animated gif time lapse.
One module is being powered and the other is not powered, just sitting
there for comparison.
These are KC125s.
The time involved here was about 3 hours and took about 1 kW-hour of
energy but gives you
an idea of what may be done with this idea. One thing not in our favor
here is that the module
that is being powered is resting on the ground, in the snow, which would
significantly
hinder snow melting I would think rather than being properly mounted.
Oh what fun it is to melt some PV snow tonight !
<a class="moz-txt-link-freetext" href="http://fusion.midnitesolar.com/PVsnowMelt3.gif">http://fusion.midnitesolar.com/PVsnowMelt3.gif</a>
boB
</pre>
<blockquote type="cite">
<pre wrap="">*From*: Mark Dickson [<a class="moz-txt-link-freetext" href="mailto:Mark@OasisMontana.com">mailto:Mark@OasisMontana.com</a>]
*Sent*: Monday, January 16, 2012 10:00 AM
*To*: 'RE-wrenches' <a class="moz-txt-link-rfc2396E" href="mailto:re-wrenches@lists.re-wrenches.org"><re-wrenches@lists.re-wrenches.org></a>
*Subject*: [RE-wrenches] Shedding ice
I recall a conversation a while back about the possibility of
"reversing" the current in a solar module to increase the cell temp
enough to shed ice/rime. To follow-up, has anybody been successful at
this? I am guessing, if so, it would entail, removal of diodes,
increasing PV and battery capacity and some way to sense the ice at
the very least. . . It sounds good in theory, but I am skeptical as to
whether it will work in reality. . .
Best regards,
Mark Dickson,
NABCEP Certified Solar PV Installer ^(TM)
Oasis Montana Inc.
</pre>
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<pre wrap="">
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